Appendix A: Previous Studies and Data Capture 7 March 2019 Page | A-1 Appendix A – Previous Studies and Data Collection Table of Contents A.1.0 Summary of Previous Studies............................................................................................................. A-1 A.2.0 Gauge Data ......................................................................................................................................... A-3 A.3.0 Vertical Datum Adjustments ............................................................................................................. A-5 A.4.0 Current Effective FEMA Studies ........................................................................................................ A-5 A.5.0 Historical Storm Events ........................................................................................................................ A-8 A.6.0 Lower Brazos River Reservoirs .......................................................................................................... A-18 A.7.0 TxDOT As-Built Bridge Plans .............................................................................................................. A-19 A.8.0 Flood Data .......................................................................................................................................... A-21 A.9.0. High-Water Marks ............................................................................................................................. A-22 A.10.0 Public Meetings ............................................................................................................................... A-22 Tables Table A-1: 2009 LJA Flood Frequency Analysis Results at Richmond, Tx Gauge .............................. A-2 Table A-2: 2009 Distributed 1% ACE Discharges in Fort Bend County ................................................. A-2 Table A-3: 2009 Fort Bend County Water Surface Elevations ............................................................... A-3 Table A-4: Lower Brazos River USGS Gauges ........................................................................................... A-4 Table A-5: Vertical Datum Adjustments by County ................................................................................ A-5 Table A-6: 1999 Brazoria County FIS Summary of Discharges .............................................................. A-5 Table A-7: 2017 Fort Bend County FIS Summary of Discharges ........................................................... A-6 Table A-8: 2017 Fort Bend County FIS Summary of Water Surface Elevations .................................. A-6 Table A-9: 2010 Austin County FIS Summary of Discharges ................................................................. A-7 Table A-10: 2010 Austin County FIS Summary of Water Surface Elevations ...................................... A-7 Table A-11: 2009 Waller County FIS Summary of Discharges ............................................................... A-8 Table A-12: 2009 Waller County FIS Summary of Water Surface Elevations ..................................... A-8 Table A-13: Hempstead Gauge Peaks (USGS ID 08111500 / 1938-2017)............................................ A-8 Table A-14: Richmond Gauge Peaks (USGS ID 08114000 / 1903-2017) .............................................. A-9 Table A-15: Rosharon Gauge Peaks (USGS ID 08116650 / 1967-2017) ................................................ A-9 Table A-16: December 1913 Flood Estimated Rainfall Totals .............................................................. A-10 Table A-17: May 1957 Flood Observed Peak Discharges ................................................................... A-12 Table A-18: 1991 Flood Observed Peak Discharges ............................................................................. A-13 Page | A-i Table A-19: 1991 Flood Reservoir Storage .............................................................................................. A-13 Table A-20: 1998 Flood Observed Peak Discharges ............................................................................. A-13 Table A-21: November 2002 Observed Peak Discharges ................................................................... A-14 Table A-22: 2004 Observed Peak Discharges ........................................................................................ A-14 Table A-23: 2007 Observed Peak Discharges ........................................................................................ A-14 Table A-24: 2010 Observed Peak Discharges ........................................................................................ A-15 Table A-25: October 2013 Flood Observed Peak Discharges ............................................................ A-15 Table A-26: May 2015 Flood Observed Peak Discharges .................................................................... A-16 Table A-27: May 2016 Flood Observed Peak Discharges .................................................................... A-17 Table A-28: T.S. Harvey 2017 Flood Observed Peak Discharges ........................................................ A-18 Table A-29: Lower Brazos River Reservoirs ............................................................................................... A-18 Table A-30: TxDOT As-Built Bridge Plans ................................................................................................... A-19 Table A-31: Progress and Public Meetings Locations ........................................................................... A-23 Figures Figure A-1: Rainfall Totals for Storm of December 1-5, 1913 End of Fifth Day ................................. A-11 Figure A-2: Brazos River Flood at Southern Pacific Railroad, Hempstead, Texas May 1, 1957 ..... A-12 Figure A-3: NASA Photo Flooding on the Brazos River on May 28, 2016 ........................................... A-22 Exhibits Exhibit A-1: USGS Gage Locations Exhibit A-2: TxDOT Bridge Plans Exhibit A-3: Highwater Marks Supporting Information Public Meeting Sign-In Sheets TxDOT Plans Highwater Mark Shapefile Page | A-ii Appendix A – Previous Studies and Data Collection A.1.0 Summary of Previous Studies Numerous studies, reports, and surveys have been completed throughout the years related to the Lower Brazos River. Documents were obtained from the Brazos River Authority (BRA), the Fort Worth District Corps of Engineers (USACE), the Texas Water Development Board, Federal Emergency Management Agency (FEMA), Texas Department of Transportation (TxDOT) and other agencies. These documents were reviewed for this study. 1. USACE Fort Bend County Study (1977) - In February 1977, a report titled “ Reassessment of 100-Year Peak Flow, Brazos River at Richmond, Texas by Espey Huston and Associates, Inc. (1984)” prepared by the USACE for the Fort Bend County Commissioners Court established the 1% ACE peak flow for the Brazos River at Richmond to be 210,000 cfs. 2. Initial Countywide FEMA Flood Insurance Study (1984) - The initial countywide hydrologic and hydraulic analyses for Fort Bend County were completed by Espey Huston and Associates for FEMA in May 1984. Espey Huston and Associates developed a methodology to re-analyze gauge data at the Brazos River at Richmond, Texas gauge (USGS ID 08114000). The methodology was developed to address the progressive development of major flood control structures within the Brazos River basin over the years resulting in a non- homogeneous streamflow data set. Recorded flows were adjusted to “unregulated flow conditions by adding the net change in reservoir storage”. The HEC-1 hydrologic computer program was utilized to produce “unregulated” flood flows to be used in the flood frequency Pearson Type III analysis. Once a satisfactory calibration had been obtained without the reservoirs, the effect of the reservoirs was incorporated and a value for each flood flow was determined. Based on this study, the 1% ACE peak flow for the Brazos River at Richmond was reduced to 181,000 cfs and applied throughout the 90 river miles in Fort Bend County. 3. Flood Protection Planning Study for the Brazos Valley Subdivision Area City of Simonton, Texas (1996) - In 1996, Claunch and Miller completed a flood protection planning study for the City of Simonton, Texas, focused on the Brazos Valley Subdivision. The study determined that the 1% ACE flood elevations near the Brazos Valley Subdivision range from 109 to 113 feet. Protection of Section I of the subdivision was determined to not be technically or economically feasible. A proposed levee system, including detention storage, diversion channel, main channel, and collector channel, was recommended for protection of Sections II and III of the subdivision. The estimated cost for the levee system (not including land acquisition) was $1.8 million in 1996. In addition to structural alternatives, it was recommended that the City’s floodplain management ordinances be revised to require new construction to be a minimum of one foot above the 1% ACE floodplain. 4. DFIRM Update for Fort Bend County, Texas (2009 ) - In 2009, the Comprehensive Flood Risk Resources and Response Joint Venture (CF3R) completed a hydrologic and hydraulic update of the Brazos River in Fort Bend County. CF3R contracted LJA Engineering and Surveying, Inc. to perform the flood frequency analysis of the USGS Richmond gauge. Analysis of the flow attenuation along the Brazos River was performed by CF3R. The 2009 LJA flood frequency analysis for the Brazos River at Richmond gauge is shown in Table